Abstract: A fabricating method of one-piece refractory metal rocket engine chamber is described. Hollow liner sections of a platinum group metal or alloy are inserted into a chamber barrel portion to form the combustion chamber, connecting into a conical portion, a venturi throat and into a second conical portion, forming an expansion nozzle exit of the chamber. The hollow liner sections correspond to the interior shapes of the chamber portions. A refractory metal split mandrel and welded end caps complete an assembly which is press formed at high temperature and pressure, undergoing a cyclic hot isostatic pressing to firmly bond the liner sections to the chamber portions. Scarfed edges of the liner sections are also bonded. The end caps and split mandrel are then machined out of the chamber and residual molybdenum removed resulting in a lined rocket engine chamber.